The present invention relates generally to gears and more particularly to novel wave gears having non-circular conjugating pitch curves and including uniform gear teeth and roots to create a tighter seal between meshing gears.
Gears used for measuring the volume of fluid flow in meters or transferring fluid in pumps are typically circular or non-circular meshing gears. In a meter, the gears are positioned within a fluid chamber of a meter housing and are journaled to seal the gear teeth against the inner walls of the chamber. The fluid chamber includes intake and outlet ports to allow for the ingress and egress of fluid. Typical meshing gears used in fluid measuring or transferring devices utilize involute gear teeth that are machined or molded to properly mesh, creating a seal between the gears. The seal created by the meshing gear teeth prevents the passage of fluid. The gears in a meter work by passing a volume of pressurized fluid through the fluid chamber. The number of revolutions of the gears is used to determine the amount of fluid that has passed through the chamber. The accuracy of the meter or pump is directly related to how well the gears are able to seal against each other and the fluid chamber. If the seal is inconsistent throughout the full revolution of the gears, the measuring device will be inaccurate since fluid will leak past the gears without producing the corresponding revolutions. Involute tooth gears, due to the inaccuracies in design, do not provide an adequate seal for precise metering between meshing gears and can agitate shear sensitive fluids. Involute tooth forms for oval gears are non-uniform throughout the perimeter of the gear and require excessive undercutting and clearances to prevent binding. This excessive undercutting and non-uniform tooth shape leads to a tooth form that does not have uniform strength and sealing surfaces around the gear""s profile. Sharp corners around teeth form high stress concentration points that weaken the gear. Gears formed with involute teeth also have varying accuracy when used for flow meters due to fluid leakage between the gear teeth, especially at low fluid flow rates. Prior art gears do not provide for a design that creates a tight seal between gear teeth to precisely measure fluid flow at low rates and reduce fluid agitation and shear.
This invention may be described as a novel wave tooth gear having a non-circular pitch curve and uniform wave teeth to create a tighter seal between meshing gears so as to provide precision metering. The term xe2x80x9cwave toothxe2x80x9d as used herein refers to a tooth profile, which if extended linearly, would result in a repeating wave pattern. The non-circular or oval wave tooth gear has a major axis and a minor axis disposed perpendicular to the major axis, wherein the major axis is longer than the minor axis. The wave tooth gear includes a central hub, a plurality of wave teeth radially extending from the gear at locations surrounding the gear and a plurality of roots, each root positioned between adjacent teeth at locations surrounding the gear. The teeth include a head portion shaped as an arc segment having a first radius and the roots include a recess shaped as an arc segment having a second radius. The teeth heads are joined to adjacent roots by lines of tangency.
Teeth and roots formed about the perimeter of the non-circular wave tooth gear are wave shaped and offer many design and manufacturing advantages. The gears have a uniform backlash throughout gear rotation due to the ability to accurately design the placement and shape of the gear teeth and roots. The wave tooth gears can be designed using Computer Aided Drafting technology, which allows the design to be easily transferred to part manufacturers. The geometric shape of the gear renders the gear easy to manufacture and prototype. Shapers and hobbing machines are not required to manufacture the gear. Meshing wave tooth gears have less sliding contact than gears of other designs, which reduces noise, wear and frictional losses. The reduced sliding contact between gears reduces the heating of metered fluid and lessens the impact on shear sensitive fluids. Hydraulic leakage between mating gears is also reduced because of a tight and consistent seal between gears. Also, the gear teeth are stronger because they are shorter and are void of sharp corners. The shorter tooth depth and lack of sharp corners allow the gears to be easily molded and extruded. The wave tooth gives the wave tooth gear a constant tooth pitch because the teeth are the same width. This makes evaluation of the velocity profile of the meshing gears easier.
These and other aspects of this invention are illustrated in the accompanying drawings and are more fully described in the following specification.